I can't tell you how to think, but, I can offer advice for how I deal with these situations.
How to put yourself first: Set boundaries. Self-explanatory.
Being hard on yourself: Accept that you will make mistakes, some that you wish that you never made, some that you were not sure if ever happen. Either way, don't be stuck in the past.
How to have a sense of humor: Can't tell you how to think.
How to make people laugh: Can't tell you how to think but don't force it.
How to flirt: Let things come naturally to you, but, pay attention to body-language, or, if the other person shows signs of interests (laughs, or, smiles, etc).
Being the convenient friend: I would recommend against this. I like settings that are more intimate. I don't like being with people simply because I'm convenient for them. But, just be easy-going, and, yourself as much as possible. I know that's terrible advice, but, don't try to be something that you're not. If you don't like who you are, change it, but for yourself, not for other people.
Being second best: There's nothing wrong with this unless you want to use it as motivation for getting better.
How to stop negative thinking: Not asking yourself all these questions all the time would probably be a good start into making you feel better and focusing on your hobbies. Look up intrusive thoughts and how to deal with them.
How to impact peoples lives: Why would it matter whether you impact people's lives or not? If you do, great, people listen. Just make sure that the other person RESPECTS you. That's what is important.
How to be an alpha: The least important thing on this list.
How to stop feeling awkward in talking: Never got over this, but, it gets better the more times you do it.
Don't let it be a wall!! Think of it like an obstacle course and you're going from one place to the next and life throws all these social obstacles in your way. You won't know what will come at any moment. So, just be prepared, don't always expect the worst, but, prepare for the worst, and hope for the best and hopefully something in-between will happen.